Convection Heat Transfer Coefficient Distribution Over the Single Rectangle Fin Surface

Rectangle fin is widely used in different kinds of heat exchangrs. Convection heat transfercoefficient distribution over the fin surface is one of the theorehcal problems in research on enhancement of heat transfer. In this paper, a tube with an attached rectangular fin is used for a model and thefin surface is divided into a network of nodes by the finite difference techinque. When the wind velocityis u= 4. 5 m/s. the temperature distribution of discretization is obtained by experimental measurement,then the convection heat transfer coefficient of all nodes are soved by using the methed of inverse heatconduction problem. Through checking with heat balance methed, the results show that the solution cancorrectly express the actual heat transfer situation.This result is useful to experimental research onenhancement of heat transfer for finned for heat exchangers.     

Experimental Study for the Movement of Liquid Droplets on the Surface with Gradient Surface Energy

By using the chemical vapor deposition (CVD), a surface with gradient surface energy is fabricated based on the treated silicon chip. The dodecyltrichlorosilane (C_(12)H_(25)Cl_3Si) and Octrytrichlorosilane (C_(8)H_(17)Cl_3Si) are used as the source of silanization. By using the measurement of sessile drop method, the surface with gradient surface energy was characterized by measuring the contact angle of small water which lied on the surface of the treated silicon chip. The experiment shows the liquid droplets are driven to move from hydrophobic to hydrophilic zone on the gradient surface which is placed horizontally, the diameter of the droplets are 1~3 mm, and the single droplet reached the maximum velocity of up to 0.9 m/s. Based on the experimental results, the mechanical of the movement of the liquid droplet on the gradient surface is researched.     

Effects of Heat Transfer Coefficient of External Window on Residential Buildings in Subtropical Areas

Using Designer's Simulation Toolkit DeST h developed by Tsinghua University, research was carried out on the energy consumption of a typical residential building in Ningbo, P. R. China, with a focus on the heat transfer coefficient of external windows facing every direction. Results show that variation of the heat transfer coefficient of external windows in all directions has a substantial effect on energy consumption for heating but little effect on energy consumption for cooling. It is difficult to decrease cooling energy consumption by decreasing the heat transfer coefficient of external windows in summer. The heat transfer coefficient of external windows facing south has a significant effect on building energy consumption, but the windows facing north have less effect, and those facing east and west have the least impact. Decreasing the heat transfer coefficient of external windows facing north and south from 4.7 to 3.2 produces the most favorable performance cost ratio for energy saving investments. Reasons for the decrease in the heat transfer coefficient of external windows leading to increased air conditioning energy consumption were discussed. The conclusions are useful for guiding energy efficient building design in other subtropical cities.     

恒速干燥阶段对流传热系数的研究

应用因次分析和实验测定相结合的方法,对恒速干燥阶段的对流传热系数进行了研究。通过实验,较精确地确定了公式中的常数,得到了形式较简捷的求取α的准数关联式。     

Experimental Study on Refrigeration Performance of Fin-tube With Circular Hole Under the Frost Condition

The performance of heat transfer of fin-tube with circular hole is better than fin-tube without hole if there is no frost,but what is the situation if under the frost condition.Tthe comparison study on performance of heat transfer and refrigeration is carriedout under the frost condition for the heat exchanger with three kinds of fins: circular and half circular hole,circular hole,plane form.The experiment process is finished through the refrigeration system of icebox.In the course of experiment,the influence of frost process to the diameter of circular hole;is analyzed The real refrigeration amount,heat transfer coefficient and real refrigeration coefficient of the three kinds of fins are compared;compare the effect of energy saving of enforced fins is given.The fin efficiency is calculated method and make out the real convection coefficient to disclose the situation of heat transfer of fins is lnade out.Results: compared with plane form fin,the following results are for fin-tube with circular hole: average heat transfer coefficient rise 11.53%,convection coefficient rises 18.84%,real refrigeration coefficient rises 6.83%,virtual refrigeration amount rises 6.02%,electricity saving is 6.39%.Fin-tube with circular hole is the best form for the three kinds of fins.     

Experimental Studies of Forced Convective Heat Transfer and Pressure Drop of Ethylene Glycol in Tubes with Three Dimensional Internally Extended Surface

In this paper,the reSults are presented from experimental investigation on heattransfer performance in seven copper tu bes with three dimensional internally extended surface(3-DIEST)varying in axial pitch,circumferential pitch,height, width and arrangement form of fins. The forced con vective heat transfer and pressure drop of ethylene glycol flowing in the 3-DLESTShave been tested in the Revnolds number range from 250 to 6,000 and the Prandtl number rangefrom 60 to 90.The average stanton number in the most superior 3-DIEST can be increased about2.4times in the laminar flow.and4.5 times in the transitional flow and turbulent flow as com-pared with that in the smooth tube. And the friction factor between fluid and tube wall can be 1.7times in laminar flow. and 4 times in transitional flow andturbulent flow inside the 3-DIEST as much as those inside the smcoth tube.     

Experiments on Convective Heat Transfer for Various Media Flowing Turbulently in Tubes with Three Dimensional Internally Extended Surface

This paper presents the experimental results of convective heat transfer performance in 5 copper tubes with three dimensional internally extended surface, with flow of various test fluid in the Reynolds number range of 8,000 to 80,000. Water and mixture of ethylene glycol with water (the ethylene glycol weight content equals 55%) are chosen as test fluid. The effect of the physical properties for test fluid on heat transfer performance in the tubes with three dimensional internally extended surface is discussed. The heat transfer correlation is obtained by the experimental data.